1. Field of Invention
The present invention relates to an ion beam processing (milling) system and ion beam processing (milling) method, enabling the prevention of redeposition of sputtered particles on a mask pattern and processed surface.
2. Description of the Related Art
As a technique for microprocessing a thin film, a beam processing is known. This beam processing is a processing method emitting (or exposing) an argon (Ar) beam or other beam on a sample at a high speed so as to shave off parts of the sample surface. As that beam processing, ion milling using Ar ions, reactive ion etching (RIE) using also chemical reactions, etc. are known.
Ion milling will be explained briefly first using FIGS. 1A to 1C.
As shown in FIG. 1A, usually a sample 301 to be processed, for example, a thin film 302 formed on the surface of a substrate, is formed with fine mask patterns 305 using a suitable resist film or inorganic material film. Next, as shown in FIG. 1B, the sample (thin film) 302 is irradiated by an argon ion beam 311 so as to etch (mill) the surface of the sample (thin film) 302 not covered by the mask patterns 305. As a result, the mask patterns 305 are transferred to the thin film 302 surface.
The problem here in that, as shown in FIG. 1C, at the time of milling, the atoms 30A at the sputtered sample surface redeposit on the aide faces of the mask patterns 305 (see FIG. 1B) and side faces of the processed parts to form so-called “burr” 321. Milled surfaces are generally cut at a slant, so the burrs 321 also deposit along those shapes. After removal of the mask patterns 305, the sectional shapes remaining resemble the floppy ears of rabbits, so are also called as “rabbit ears”. The heights of the burrs 321 reach as much as the thicknesses of the mask patterns 305 depending on the milling conditions. They are also not necessarily proportional to the milling amounts. With even a slight milling depth, for example, about 20 nm, burrs often become extremely great in height, for example, 100 to 200 nm. These burrs 321 deposit at the side faces of the processed surfaces, so when etching a multilayer film, easily cause interlayer short-circuits and cause the inherent functions of the device to be lost, for example, see Japanese Unexamined Patent Publication (Kokai) No. 11-289058; Hiroshi GOHEI and Sotaro EISHO ed., Vacuum, vol. 20, no. 11, p. 17 to 25, 1977 (in Japanese); and Per G. Gloersen ed., J. Vac. Sci. Technol., vol. 12, no. 1, p. 28 to 35, 1975.
For example, frequent use is made of the process of using a resist for a mask pattern and burying it with an insulating film 331 as shown as FIG. 2A, then lifting it off as shown in FIG. 2B. In this case, if a burr 321 covers the side faces of the mask pattern 305, peeling off the mask pattern 305 will become difficult. That is, liftoff will become difficult.
Further, as shown in the top view of FIG. 3A and the sectional view of FIG. 3B, the burr 321 grows slanted inward, so residue 333 of the resist easily occurs at the root part. A contact hole is formed on the top surface of the device by liftoff, but the size of the opening will end up becoming smaller than the design size due to the burr 321. If the size of the device is on the submicron order, the ratio of the burr 321 in the contact hole part will become remarkably high and make formation of an opening difficult. The occurrence of burrs 321 becomes more remarkable the smaller the mask size. The height and thickness of the burrs increase. Further, at the time of liftoff or peeling of a mask pattern, the percentage of a burr 321 removed together with the mask pattern will also drop. Therefore, the damage caused by the burr 321 becomes more remarkable the smaller the device size.
As explained above, in the ion milling of the related art, due to burrs formed at the timing of milling (redeposition of sputtered particles), the microprocessing capability was limited. It is becoming difficult to answer the demands for further miniaturization to the submicron and nanometer (mm) order required for future production of semiconductor devices, micro electro mechanical systems (HEMS), etc.
As one means for dealing with this, use has been made of the technique of removing burrs formed while milling a sample surface by exposing an ion beam on the sample surface at a slanted direction (direction inclined tens of degrees from direction perpendicular to sample surface), but the effect of removal is small. Further, the problem arises of increased tapering at the cross-sectional profile of the milling.